1. Field of the Invention
The invention relates to sandwich boards. Sandwich boards are panels which are hinged together at a top generally horizontal surface so that they may be folded flat or opened into a roof shape. Usually they are used for advertising purposes. The invention especially relates to free standing sandwich boards.
2. Description of the Prior Art
Sandwich boards have traditionally been made from any rigid flat material such as fibre board, chip board, wood, etc. Such sandwich boards utilize metal hinges and, where the board is attached to a frame, metal nails or staples or screws. The combination of materials used generally makes the sandwich boards unsuitable for recycling. Moreover, they tend to be heavy and also tend to deteriorate in bad weather conditions especially in rain.
The use of plastic materials for sandwich boards has been considered but plastic materials such as polyethylene have been considered to have had sufficient obvious disadvantages to cause their potential use to be viewed with disfavour.
Disadvantages of polyethylene which, when taken together, cause polyethylene to be viewed as an unsuitable material for forming sandwich boards are, for example, difficulty in printing on polyethylene, warping of polyethylene in varying temperature conditions, or the lightness of polyethylene.
Although the difficulty in printing on plastic materials has been largely overcome in many fields, the production of sandwich boards often require use of very easily available printing inks or paint. Economically, it has not been considered viable to utilize the specialized printing inks which are necessary for printing on plastics.
Warping of sheet plastic materials under varying temperature conditions causes bowing or dishing of the surface with consequent distortion of the subject matter printed on it. If the surface warps before the printing is to take place then the advertising material is permanently distorted and unacceptable.
Although the heaviness of the traditional sandwich boards is held against them, the extreme lightness of plastics material sandwich boards makes them liable to be blown away in windy conditions or blown over.